Astronomers can be their own worst enemies. Just a few days ago we were encouraged to take our binoculars outside and point them above the end stars of handle of the Plough to see an exploding star, a supernova, in the galaxy M101, 21 million light years away.

This is the brightest supernova in Britain's sky for at least 18 years, but it was shining (and may still be shining) at magnitude 10, beyond the grasp of any but the largest of binoculars, even without the bright moonlight at present. In fact, we probably need a telescope and a decent chart just to glimpse it near the galaxy's SSW fringe. To suggest otherwise is misleading and has probably left many people frustrated.

Sometimes astronomy is misrepresented in support of silly fringe ideas. One of the strands of nonsense associated with the claims of an impending catastrophe in 2012 is that an object, sometimes called Planet X or Nibiru, will collide with the Earth, or sweep close enough to trigger a cataclysm. Astronomers know this to be fiction, but when the Russian amateur observer Leonid Elenin discovered a comet last December the catastrophists soon linked it with the Nibiru story.

Comet Elenin was beyond Jupiter when it was found, but tracking inwards towards a perihelion 72 million km from the Sun, which it passed on Saturday. It is now tracking outwards and will pass a safe 35 million km from the Earth on 16 October. Despite the claims to the contrary, there is no chance of a collision or of any of the other dire effects we read about. Indeed, the comet's nucleus was only ever a small icy body and observations suggest that it may have disintegrated as it neared perihelion, as others have done before.

Our chart shows the lower half of our eastern sky at 05:30 BST tomorrow, but is valid also for 03:30 BST in mid-October. Mercury is just visible tomorrow, very low in the twilight at mag -1.1, but is likely to disappear by next weekend.

The diagonal lines show the paths of Mars and of Comet Elenin, with tick marks to show the positions of Mars and the comet every 10 and five days respectively. Mars is unmistakable below Castor and Pollux at present, reddish in hue and brightening from mag 1.4 tomorrow to 1.0 on 10 November when it passes 1.4° N of Regulus in Leo. On the way, it passes in front of the Praesepe star cluster on 1 October and lies near the waning Moon on 23 September and 22 October. If enough remains of the comet, it may still be visible during October and perhaps even through binoculars, though I fear we will be disappointed.